Problems arise with such ram-boring machines if they must be removed from a bore after getting stuck or when thrust bores are produced. In this case, it must be ensured that the change-over from forward motion to reverse motion can be easily realized, and that the restarting of the ram-boring machine is ensured. This also applies to instances in which the ram-boring machine has penetrated very far into the ground. In known ram-boring machines, the change-over from forward motion to reverse motion is realized by axially displacing a control tube. If this axial displacement is realized by means of compressed air after releasing a locking mechanism of the control tube, it is possible to change the ram-boring machine from forward motion to reverse motion without having to interrupt the compressed air supply. However, another change-over from reverse motion to forward motion requires an interruption of the compressed air supply because the control tube cannot simply be retracted into its forward motion position due to the high air pressure. However, it is particularly disadvantageous to interrupt the compressed air supply of the ram-boring machine during the change-over because the percussion piston can assume dead center positions in the housing and an automatic restarting from these dead center positions may not be possible. When changing the motion while the compressed air supply is interrupted, the forward and backward motion of the percussion piston is also interrupted, i.e., it is possible that the ram-boring machine cannot be restarted after the change-over.
Another known change-over method utilizes a control sleeve that engages into the percussion piston as well as a coaxial, rotatable control tube that cooperates with the control sleeve and causes the change-over from forward motion to reverse motion. However, this known method requires seals between the housing and the percussion piston, between the percussion piston and the control sleeve, and between the control sleeve and the control tube, i.e., the number of seals that are subjected to wear is relatively high.